It is generally known to a person skilled in the art of propeller drives of aircraft that adjustable propeller blades of aircraft propellers serve to optimize the propeller efficiency in order to obtain an optimum propeller blade position for all propeller speeds. For this reason, it is necessary to individually fasten the propeller blades of the aircraft propeller to the propeller hub and, for facilitated adjustability, to mount said propeller blades in corresponding rolling bearings. A propeller blade bearing arrangement of said type is for example known from the British patent GB 2 244 525 A and is composed substantially of a propeller hub, to which a plurality of propeller blades are individually fastened in a corresponding number of blade receptacles of a blade carrier ring. Each propeller blade has, at its blade root, a primary adjustment bearing and a secondary adjustment bearing and is longitudinally axially mounted within a blade receptacle so as to be rotatable, with both the primary adjustment bearing and the secondary adjustment bearing being designed as angular rolling bearings which are arranged so as to be longitudinally axially spaced apart from one another and are braced against one another. Both adjustment bearings have one upper race and one lower race each and a row of rolling bodies which are arranged between said races, with the primary adjustment bearing being formed in a physical embodiment by an angular contact ball bearing, while the secondary adjustment bearing is designed as an angular roller bearing. In order to lubricate the entire adjustment mechanism for the propeller blades, a lubricating oil reservoir is arranged in the propeller hub, from which lubricating oil reservoir the primary and the secondary bearings are also supplied with lubricating oil by means of centrifugal force as the propeller rotates in order to avoid wear.
The assembly of the known propeller blade bearing arrangement takes place substantially in such a way that a bearing support sleeve, which surrounds the blade root of the propeller blade and forms in each case the seat of the upper races of the adjustment bearings, is initially assembled in two halves on the blade root, before the upper bearing rings, which are likewise composed of two halves, of the adjustment bearings are placed on said bearing support sleeve and can be connected in a suitable way to form continuous rings. A two-part cage is subsequently placed around the upper race of the secondary adjustment bearing and connected to form a ring, so that the rolling bodies of the secondary adjustment bearing can be inserted into the cage. A sleeve which partially has a thread at the outer side and, in the assembled state, forms, with a part of its inner side, the lower running track of the secondary adjustment bearing, is then pushed loosely, together with a cage for the rolling bodies of the primary adjustment bearing, over the blade root of the propeller blade, and the rolling bodies of the primary adjustment bearing are subsequently inserted into the cage. The loose sleeve on the blade root is thereafter pulled over the rolling bodies of the secondary adjustment bearing until said sleeve bears at the inside against said rolling bodies as a lower race, and subsequently, a two-part blade receptacle which, at the inside, contains the likewise two-part upper race of the primary adjustment bearing, is braced around the blade root in such a way that the upper race of the primary adjustment bearing rests on the rolling bodies of the latter. Finally, a threaded bracing ring which is supported against the assembled blade receptacle is screwed onto the thread of the sleeve, which is loose up until that time, on the blade root, so that on the one hand the outer race of the secondary adjustment bearing, which is formed by the inner side of the loose sleeve, is braced against the rolling bodies of the latter, and on the other hand, the two adjustment bearings of the propeller blade bearing arrangement are braced against one another. At the same time, the point at which the blade root emerges from the blade receptacle is sealed off in an oil-tight fashion by means of two seals which are arranged between the sleeve, which is designed at the inner side as a lower bearing ring of the secondary adjustment bearing, and the bearing support ring, and also between said sleeve and the blade receptacle.
A disadvantage of said known propeller blade bearing arrangement is, however, that the specific arrangement and design of the adjustment bearings for the propeller blade requires a largely two-part design of the entire propeller bearing arrangement, as a result of which a multiplicity of individual parts are required for each propeller bearing arrangement, which above all disadvantageously increases the risk of errors in their assembly. Since said individual parts must additionally be produced extremely precisely and with fitting accuracy with respect to one another, there is also a considerable time and cost expenditure for the assembly of the propeller blades to the propeller hub in addition to the high expenditure for production, so that a propeller blade bearing arrangement of said type entails very high overall production costs. Furthermore, from a safety-related point of view, a considerable disadvantage of said known propeller blade bearing arrangement is that the lubricating oil, which rises out of the lubricating oil reservoir in the propeller hub as a result of centrifugal force as the propeller rotates, can flow unhindered through the two adjustment bearings, and therefore at high propeller speeds, bears with a pressure which corresponds to the centrifugal acceleration against the two seals which are arranged at the point at which the blade root emerges from the blade receptacle. This can, in the case of a damaged seal at one of the propeller blade bearing arrangements of the aircraft propeller, lead to the loss of the entire quantity of lubricating oil in the propeller hub, which can result in failure of lubrication in the adjustment mechanism and the adjustment bearings of the propeller blade bearing arrangement as well as in function failures while the aircraft is in operation.